The invention relates to a radiation-sensitive semiconductor device comprising a semiconductor body which at a substantially flat surface comprises at least one radiation-sensitive diode having at least two sub-elements of which at least one has a connection to provide a signal proportional to the radiationgenerated current through the sub-element.
A radiation-sensitive diode may be understood to be a photodiode or, for example, a radiation-sensitive base-collector junction of a photo-transistor or other radiation-sensitive semiconductor junctions or metal-to-semiconductor junctions. In the case of a photo-transistor the connection to record the generated current is usually connected to an emitter of the photo-transistor.
Radiation-sensitive semiconductor devices of the above-mentioned kind are used, for example, in photosensitive circuits for displaying pictures and in devices for track-following or positioning light beams (or beams of different wavelengths of radiation). Applications other than radiation detection are in the field of spectroscopic analysis, notably in the wavelength range from 200-1100 nanometers and, for example, soft X-ray radiation. In addition such devices are used for the detection of particle radiation (for example, electrons and .alpha.-particles).
In existing radiation-sensitive devices, for example quadrant diodes, the sub-elements are formed by semiconductor zones which are situated at the surface of the semiconductor body and which have a connection to record the photoelectric current through the sub-element and which form rectifying junctions with the surrounding part of the semiconductor body. When the radiation-sensitive diode is reverse biased, depletion regions are present at the area of the sub-elements in the semiconductor body (and in the semiconductor zones). In said depletion regions an electric field which is determined substantially entirely by the voltage across the diode prevails. When charge carriers are generated in the depletion regions as a result of incident radiation, said carriers contribute to a photo-electric current through the sub-elements under the influence of the prevailing electric field.
In such radiation-sensitive semiconductor devices there is the problem of crosstalk between the sub-elements. In existing devices this problem has been solved by providing a sufficiently large spatial separation between the sub-elements and the associated depletion regions. Charge carriers which are generated in or near the depletion region of a sub-element then substantially do not contribute to the photoelectric current through other subelements.
However, such a spatial separation is at the sacrifice of the resolving power of the device: notably, narrow beams or small displacements of a beam between two sub-elements are not clearly detected as a variation in the photoelectric current through adjacent sub-elements.
Charge carriers are also generated between the depletion regions. These can either disappear by recombination or reach a depletion region of a sub-element by diffusion and provide a contribution there to the photoelectric current. This contribution is slower and can moreover reach sub-elements other than the adjacent ones.
In U.S. Pat. No. 3,858,233, measures are suggested to cause radiation which is incident approximately centrally between two sub-elements to provide a substantially negligible contribution to the photoelectric current. For this purpose, a layer of radiation-absorbing material is provided between adjacent elements over at least a part of the surface present between the sub-elements. In this manner, a separation strip is formed between two sub-elements where incident radiation does not reach the semiconductor surface.
As a result of the presence of a radiation-absorbing layer, radiation which is incident at the area of said layer does not contribute or hardly contributes to a photoelectric current. This reduces the sensitivity of such a device.